Creature from the Haunted Sea (1961)

After political unrest breaks out on a Caribbean island, scheming criminal Renzo Capetto (Anthony Carbone) sees an opportunity. He promises to transport a group of exiles out of the country while also taking part of the national treasury. Followed onto the boat by an American agent (Edward Wain), Capetto plans to kill off the exiles and explain that their deaths were from a sea monster. Then he can keep the money for himself. But this plan goes awry when the sea monster actually shows up.